The invention relates to industrial filtration systems and in particular to an improved nozzle construction for use in multiple in a filtration system, such as a sand-filter underdrain system.
A modern gravity-operated filter construction relies upon a horizontal tube sheet having a plurality of like openings to each of which a tubular plastic nozzle is fitted and retained by snap engagement, upon insertion from below, i.e., from the downstream side of the tube sheet. Each nozzle is open at both ends, and there is thus substantial upwardly open exposure for occasional passage of or clogging by solid matter. To foreclose entry for such passage or clogging, it is customary to employ vertical spacers on the tube sheet whereby a support grid can be positioned at or slightly above the snap-engaged upper ends of the nozzles; the support grid retains a gravel bed free of the upstream ends of the nozzles, and sand, anthracite coal, or other granular media may provide successive beds of filter material carried by the gravel bed.